Interpretive Summary: Viral diseases are often the primary cause of mortality in commercial chickens. Viruses are generally controlled either by eradication of the virus from breeder flocks, or by development and use of vaccines. However, another basic factor that influence's the growth of a virus is the production by infected cells of a protein termed interferon. Interferon was first discovered in chickens, and protects animal cells from infection by additional viruses. In this paper we describe methods showing that blood cells from chickens of different unique breeding strains produce different quantities of interferon. It is anticipated that these genetic differences in production of interferon will affect resistance to viral infection, and may influence response to viral vaccines. It is postulated that further studies will define the hereditary units, i.e. genes, controlling the level of interferon production. If poultry breeders could directly select chickens with genes for optimal interferon production this could improve resistance to viral induced diseases.

Technical Abstract:
Interferon (INF) was evaluated in the supernatants from peripheral white blood cells (WBC) of chickens from six lines. The WBC were cultured in flasks or 24-well plates with medium, or medium and phytohemagglutinin (PHA). After 2-5 days duplicate supernatant samples were tested for INF; i.e. the log2 titer inhibiting 50% destruction of the cytopathic effect of vesicular stomatitis virus on primary chick embryo fibroblasts. Also triplicate WBC samples were tested for proliferation by [H3]-thymidine labeling and scintillation counting. In the absence of PHA, INF was significant (P<0.05) for only two lines, i.e. 72 (two trials) and C (one trial). With PHA the level of INF produced was similar if flasks were sampled daily, or on successive days. INF levels were highest using 10 or 20 mg/ml PHA, but line differences were best distinguished using 5 or 10 mg/ml. In three trials there was a low correlation between PHA stimulated WBC proliferation and INF titer (r2 > 0.30; P< 0.05). We conclude that supernatants from chicken WBC stimulated with 10 mg/ml PHA contain INF, and inbred lines 72 and C repeatedly produce more INF than inbred lines 63 and 15I5. This is the first evidence for line differences in INF production in chickens, and these lines may be useful for characterization of the relevant genes and their importance in immune response(s) and disease resistance.